Department of Biological Sciences

Biodegradable Magnesium Alloys: A Review of Material Development and Applications

Dharam Persaud et al. — Wed, 07 Mar 2012 09:15:17 PST

A natural history of the Ramayana

David W. Lee — Wed, 21 Dec 2011 09:00:41 PST

Iridescent blue plants. Some tropical plants produce color as insects do, using layered filters to create patterns of ligth interference. The filters' adaptive value remains a mystery.

David W. Lee — Wed, 21 Dec 2011 07:47:20 PST

Why leaves turn red. Pigments called anthocyanins probably protect leaves from light damage by direct shielding and by scavenging free radicals

David W. Lee et al. — Wed, 21 Dec 2011 06:50:51 PST

Are mangroves in the tropical Atlantic ripe for invasion? Exotic mangrove trees in the forests of South Florida

James W. Fourqurean et al. — Mon, 19 Dec 2011 09:59:59 PST

Two species of mangrove trees of Indo- Pacific origin have naturalized in tropical Atlantic mangrove forests in South Florida after they were planted and nurtured in botanic gardens. Two Bruguiera gymnorrhiza trees that were planted in the intertidal zone in 1940 have given rise to a population of at least 86 trees growing interspersed with native mangrove species Rhizophora mangle, Avicennia germinans and Laguncularia racemosa along 100 m of shoreline; the population is expanding at a rate of 5.6% year-1. Molecular genetic analyses confirm very low genetic diversity, as expected from a population founded by two individuals. The maximumnumber of alleles at any locus was three, and we measured reduced heterozygosity compared to native-range populations. Lumnitzera racemosa was introduced multiple times during the 1960s and 1970s, it has spread rapidly into a forest composed of native R. mangle, A. germinans, Laguncularia racemosa and Conocarpus erectus and now occupies 60,500 m2 of mangrove forest with stem densities of 24,735 ha-1. We estimate the population growth rate of Lumnitzera racemosa to be between 17 and 23% year-1. Populations of both species of naturalized mangroves are dominated by young individuals. Given the long life and water-dispersed nature of propagules of the two exotic species, it is likely that they have spread beyond our survey area. We argue that the species-depauperate nature of tropical Atlantic mangrove forests and close taxonomic relatives in the more species-rich Indo-Pacific region result in the susceptibility of tropical Atlantic mangrove forests to invasion by Indo-Pacific mangrove species.

Physical basis and ecological significance of iridescence in blue plants

David W. Lee et al. — Mon, 19 Dec 2011 07:46:18 PST

Genetic variation in wild populations of rain-forest trees

Yik-Yuen Gan et al. — Thu, 15 Dec 2011 09:29:25 PST

Epidermal cells functioning as lenses in leaves of tropical rain-forest shade plants

Richard A. Bone et al. — Thu, 15 Dec 2011 09:14:02 PST

A ray tracing model has been developed to investigate the possible focusing effects of the convexly curved epidermal cell walls which characterize a number of shade-adapted plants. The model indicates that such focusing occurs, resulting in higher photosynthetic photon flux densities at certain locations within the leaf. It is postulated that there will be a corresponding increase in the rate of photosynthesis. In addition, leaf reflectance measurements indicate that this is generally less for the shade plants compared with sun species and would be advantageous in increasing the efficiency of energy capture. Either effect is important for plants which must survive at extremely low light levels.

Optical properties of leaves of some Indian plants

David W. Lee et al. — Thu, 15 Dec 2011 08:51:53 PST

Ultrastructural basis and function of iridescent blue colour of fruits in Elaeocarpus

David W. Lee — Thu, 15 Dec 2011 07:54:40 PST

Iridescent colour, caused by physical effects (thin-film interference, diffraction and Tyndall scattering), is relatively common in animals but exceedingly rare among plants¹. Some benthic marine algae produce blue to violet iridescence^2,3, and the upper leaf surfaces of a few vascular plants from the shady environments of humid tropical forests are iridescent blue^4–6. Blue fruit colour has been assumed to be caused by anthocyanins⁷. A survey of such fruits (26 species in 18 genera) in Costa Rica, India, Florida and Malaysia, showed this to be the case, except for the iridescent colour in fruits of Elaeocarpus angustifolius Blume (Elaeocarpaceae). There I show that the colour is caused by a remarkable structure in the epidermis, and provide evidence for its selective advantage.

Why leaves are sometimes red

Kevin S. Gould et al. — Thu, 15 Dec 2011 07:23:39 PST

The biology of rudraksha

David W. Lee — Thu, 15 Dec 2011 07:02:23 PST

Rudraksha, used throughout India and Southeast Asia in religious jewellery, is the stony endocarp of a tree distributed from northern Australia to southern Nepal. This article summarizes its biology, particularly recent research on the remarkable fruit colour. The iridescent blue colour is caused by a remarkable structure an 'iridosome'. It is secreted by the epidermal cell, and is located above the plasmalemma and beneath the adaxial wall. Cellulosic layers within the iridosome constructively interfere with blue wavelengths, causing an intense colour production at 439 nm. This colour persists in senescing fruits and may enhance their dispersal. The transparency of the cuticle at longer wavelengths allows photosynthesis to occur in the fleshy green exocarp tissue, enhancing the carbon balance of the tree. More research will certainly reveal the evolution of this remarkable phenomenon, as well as the origins of the rudraksha's cultural use.

Cascading ecological effects of low-level phosphorus enrichment in the Florida Everglades

Evelyn E. Gaiser et al. — Wed, 14 Dec 2011 13:54:32 PST

Few studies have examined long-term ecological effects of sustained low-level nutrient enhancement on wetland biota. To determine sustained effects of phosphorus (P) addition on Everglades marshes we added P at low levels (5, 15, and 30 µg L^-1 above ambient) for 5 yr to triplicate 100-m flow-through channels in pristine marsh. A cascade of ecological responses occurred in similar sequence among treatments. Although the rate of change increased with dosing level, treatments converged to similar enriched endpoints, characterized most notably by a doubling of plant biomass and elimination of native, calcareous periphyton mats. The full sequence of biological changes occurred without an increase in water total P concentration, which remained near ambient levels until Year 5. This study indicates that Everglades marshes have a near-zero assimilative capacity for P without a state change, that ecosystem responses to enrichment accumulate over time, and that downstream P transport mainly occurs through biota rather than the water column.

Unravelling the evolution of autumn colours: an interdisciplinary approach.

Marco Archetti et al. — Wed, 14 Dec 2011 12:43:24 PST

Leaf colour change is commonly observed in temperate deciduous forests in autumn. This is not simply a side effect of leaf senescence, and, in the past decade, several hypotheses have emerged to explain the evolution of autumn colours. Yet a lack of crosstalk between plant physiologists and evolutionary ecologists has resulted in slow progress, and so the adaptive value of this colour change remains a mystery. Here we provide an interdisciplinary summary of the current body of knowledge on autumn colours, and discuss unresolved issues and future avenues of research that might help reveal the evolutionary meaning of this spectacle of nature.

Plant secondary compounds in the canopy and understorey of a tropical rain forest in Gabon

Kelsey Downum et al. — Wed, 14 Dec 2011 12:43:23 PST

Using bottles to study shade responses of seedlings and other plants

David W. Lee et al. — Wed, 14 Dec 2011 10:57:55 PST

We briefly review the nature of light and its effects on plants, and then describe an inexpensive experimental system for studying the effects of shade, specifically the contributions of reduced intensity ("quantity") and the altered spectral distribution of foliage shade ("quantity") on the development of seedlings and other plants. This system has been devised to be safe to construct, inexpensive in its use of readily available materials, and appropriate for a range of student grade levels, from ~grade six to university courses in botany. We conclude by suggesting a range of experiments this system will allow. An advantage of this system is that it promotes the study of the responses of a large range of plants, most completely unstudied for these responses.

Three birds with one stone: moas, heteroblasty and the New Zealand flora.

David W. Lee et al. — Wed, 14 Dec 2011 10:19:46 PST

Animal pigment bilirubin discovered in plants

Cary Pirone et al. — Wed, 14 Dec 2011 10:19:45 PST

The bile pigment bilirubin-IXα is the degradative product of heme, distributed among mammals and some other vertebrates. It can be recognized as the pigment responsible for the yellow color of jaundice and healing bruises. In this paper we present the first example of the isolation of bilirubin in plants. The compound was isolated from the brilliant orange-colored arils of Strelitzia nicolai, the white bird of paradise tree, and characterized by HPLC−ESMS, UV−visible, ¹H NMR, and ¹³C NMR spectroscopy, as well as comparison with an authentic standard. This discovery indicates that plant cyclic tetrapyrroles may undergo degradation by a previously unknown pathway. Preliminary analyses of related plants, including S. reginae, the bird of paradise, also revealed bilirubin in the arils and flowers, indicating that the occurrence of bilirubin is not limited to a single species or tissue type.

Anthocyanins in Leaves and Other Vegetative Organs: An Introduction

David W. Lee et al. — Thu, 01 Dec 2011 10:56:50 PST

Although anthocyanins are most recognized as pigments contributing to coloration in fruits and flowers, they are also present in leaves and other vegetative organs. Although their presence has long been recognized, particularly because of their contribution to autumn coloration, the phenomenon has been poorly studied and is not well understood. In this chapter we review the history of research on anthocyanins in leaves, emphasizing the flurry of research at the end of the 19 th century as well as the growing body of contemporary research on the topic. We emphasize the various hypotheses of anthocyanin function that were mainly developed more than a century ago, and emphasize recent research that takes advantage of our dramatically increased understanding of whole plant physiology.

Anthocyanins in Autumn Leaf Senescence

David W. Lee — Thu, 01 Dec 2011 10:02:38 PST

Anthocyanins are synthesized during leaf senescence in certain plants across virtually all biomes, but are most spectacular in the autumn foliage of temperate deciduous forests. The patterns of color production in senescing foliage depend at least partly upon species composition and their phenology. Both ecological and physiological explanations have been raised to explain why plants produce this pigment just before leaf fall. Physiological explanations, as photoprotection, predict that cyanic leaves would be better able to resorb nitrogen during the process of chlorophyll degradation. Ecological explanations predict better dispersal of propagules advertised by association with the brilliantly colored leaves (plausible for only a minority of species), or warning against egg-laying activity of herbivorous insects, as aphids. These hypotheses make predictions that we now can test, to help us understand this old mystery - and majestic phenomenon.